The present invention relates to a device for locking selectors on the bottom of needle cylinder grooves in circular knitting machines.
As is known, circular knitting machines for manufacturing stockings, knitwear and the like, have selectors which are accommodated in the grooves of the needle cylinder below the needles. Said selectors have, proximate to their lower end, a heel directed towards the outside of the needle cylinder which can be engaged with a crown cam which extends around the needle cylinder and has rising portions alternated with descending portions to raise the selectors in a direction parallel to the axis of the needle cylinder so that said selectors raise, in turn, the overlying needles to put them to work, that is to say to directly or indirectly determine the takeup of the thread by the overlying needles.
In practice the choice of the selectors which are to engage with the crown cam determines which needles are to be put to work, unless a subsequent selection is performed; said selection may be performed directly on the needles if needles having long or short heels, engageable or not with movable cams provided around the needle cylinder, are used.
In many types of machine the choice of selectors is performed upstream of each rising portion of the crown cam, which portion is in turn arranged upstream of a feed or drop of the machine, by means of an extraction cam which acts on the selectors, causing the protrusion of their lower end, or at least of the heel arranged proximate thereto, from the related groove of the needle cylinder. The extraction cam may be provided proximate to the upper end of the selectors and act radially from the outside in the direction of the axis of the needle cylinder, or proximate to the lower end of the selectors and act radially from the inside towards the outside; in both cases the selectors have, on their side directed towards the axis of the needle cylinder, a configuration adapted to rest on the bottom of the related groove of the needle cylinder and to allow the selectors an oscillation in radial planes which pass through the axis of the needle cylinder.
Between the extraction cam and the subsequent rising portion of the crown cam, selection devices are provided which, according to the knitting to be performed, are controlled by a machine control element and contact the selectors corresponding to the needles which are not to be put to work, inserting them into the related grooves of the needle cylinder so that their heel, arranged proximate to the lower end, does not engage with the crown cam but passes internally thereto. To allow a considerable possibility of selection, the selectors have, above the heel located proximate to the lower end, a plurality of heels alternated with recesses, and the selection devices generally consist of rods or levers which are actuated so as to interfere or not interfere with said heels to return the related selector to its sunk position or to leave it in extracted position.
If no needle selection is required, i.e. if all the needles are to be put to work or if the selection is performed directly by means of the cams which engage the heels of the needles, all the selectors are inserted into the related grooves before the rising portions of the crown cam. This fact can be obtained by making the extraction cams controllably movable in a radial direction with respect to the needle cylinder, so that when the selectors are not to be used said cams can be moved away from the selectors so as to not interfere therewith, or by extracting and inserting all the selectors successively.
In current circular knitting machines for stockings with rotating needle cylinder, the high rotation speed determines a centrifugal force which tends to move the selectors to their extraction position even without the intervention of the extraction cams. If the extraction of the selectors by centrifugal force occurs downstream the selection devices and before the rising portions of the crown cam, it may occur that the selectors engage with the crown cam, determining errors in the knitting being performed.
Even if this extreme condition does not occur, the selectors continuously contact the levers of the selection devices and the inner side of the crown cam, creating countless wear and breakage problems which considerably limit the life of the selectors and the elements of the machine contacted thereby.